1. Field of Invention:
This invention relates to and has among its objects the provision of novel methods for heating a liquid containing heat coagulable proteinaceous material to a temperature above the coagulation temperature of the protein. Further objects of the invention will be evident from the following description where parts and percentages are by weight unless otherwise specified.
2. Description of the Prior Art:
In the processing of many liquids containing heat coagulable proteinaceous material, it is often necessary to heat the liquid to a temperature above the coagulation temperature of the proteins in the liquid and thereby precipitate the proteins contained therein. Conventionally, steam is injected into the liquid to raise its temperature to the desired point. During treatment with steam the amount of water in the liquid being heated is increaased, often by 12% or more. Frequently, the water added during the steam injection step must be removed, and thus the time expenditure and energy requirements of the drying process per unit weight of product is increased. In addition, the volume of water added from steam injection reduces the production capacity of the equipment by this volume, so that, when steam injection is used, additional capital expenditure for larger capacity equipment is required to process the equivalent amount of material as that when steam injection is eliminated.
It is possible to avoid steam injection and raise the temperature of the liquid by employing a solid surface heat exchanger. The term "solid surface heat exchanger" is used synonymously with "heat exchanger" and is defined as a device to transfer heat from a heat source to a cooler liquid by means of a heat transferring solid surface. The heat source used to heat the solid surface may be a heated fluid, electricity or the like.
Problems result when a liquid containing heat coagulable proteinaceous material is introduced into a heat exchanger for the purpose of raising the liquid temperature above the protein coagulation temperature. During such heating processes, the hot heat exchanger wall becomes rapidly coated with protein substances which decrease the ability of the heat exchanger to transfer heat from the heat source to the cooler liquid thus destroying the efficiency of the heating process. As the heat exchanger becomes coated or fouled, the heat transfer coefficient declines steadily and rapidly so that the temperature of the liquid to be heated can be raised to the desired level so as to coagulate the remaining protein only after prolonged application of heat which is economically prohibitive.
Mechanically aided heat exchangers equipped with blades attached to a rotor to continuously scrape the heat exchanger surface and remove the fouling film are available for commercial use. However, this type of equipment is expensive and unreliable. Furthermore, high maintenance costs are required to keep such exchangers operable. Also, in the processing of some liquids containing heat coagulable proteinaceous material such as the waste water from potato processing, the extreme fouling which results from heating in a heat exchanger often can not be removed by cleaning in-place procedures and laborious and costly manual scraping is necessary.